In order to meet the increasing demand for wireless data traffic since the commercialization of 4G communication systems, the development focus is on the 5th Generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post Long Term Evolution (LTE) system.
Consideration is being given to implementing the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive MIMO, Full Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna.
Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud Radio Access Network (cloud RAN), ultra-dense network, Device to Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation.
Furthermore, the ongoing research includes the use of Hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM) (FQAM) and Sliding Window Superposition Coding (SWSC) as Advanced Coding Modulation (ACM), Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA).
With the popularization of smartphones, data traffic is increasing rapidly. The increasing number of smartphone users spurs the consumption of smartphone-based application services such as Social Network Service (SNS) and gaming service, resulting in even greater increases in data traffic. In particular, the expansion of communication between intelligent things (such as person-to-machine communication and machine-to-machine communication), which is emerging as a new communication paradigm beyond the legacy person-to-person communication, is likely to produce an unbearable concentration of traffic to base stations.
There is therefore a need of a technology to solve such problems, and direct communication between devices is coming into the spotlight as one of such technologies. This technology, so called Device to Device (D2D) communication, is promising because it is compatible with both the licensed band communication system such as the cellular communication system and the unlicensed band communication system such as the Wireless Local Area Network (WLAN) system.
In a communication environment where networks of multiple operators coexist, there is a need of an inter-operator D2D discovery service. In order to advertise a local area advertisement to the terminals camped on the networks of different operators, the use of a contents server can be considered to assist the legacy D2D discovery scheme.